Acid base indicators are used to determine which solution is an acid and which is a base. As discussed in the chemical and physical properties of acids and base we discussed how acids and bases will change the colour of certain solution or papers. These paper and solutions are called INDICATORS.

There are a lot of indicators which includes

• litmus solution (litmus paper)

• methyl orange

• methyl red

• phenolphthalein

The above mentioned indicators changes colour when it comes into contact with an acid or a base.

INDICATOR.                  ACID.               BASE

litmus paper.            Red/pink.            blue

Methyl orange.              Red.               yellow

Phenolphthalein.       Colourless.       red

The PH

The acid base indicators are used to differentiate between an acid and a base. Nonetheless it’s very difficult to use the indicators to differentiate between acids if they are all strong or weak and/or bases if they are all strong or weak. we basically can’t also use the H+ or OH- because their concentrations are small in solution.

Due to this difficulty the pH meter is used to measure the pH of the solution. This pH tells whether the solution in question is an acid or a base and again it is able to differentiate between an acids and a base even when they are all strong acid or weak acids.

The pH meter works with the pH scale. This is a scale of 0- 14.

A substance with a pH that falls between 0 -7 is an acid.

A substance with a pH that falls between 7-14 is a base.

A substance with the pH falling at exactly 7 is a neutral solution. this show that solution is neither an acid nor a base.